The present invention pertains to an exposed lens retroreflective article that includes a colored layer that has a dye that is covalently bonded to a polymer.
Persons who work or exercise near motor vehicle traffic can be made safer by wearing clothing that highlights the person""s presence to passing motor vehicles. To promote the safety of roadway workers and pedestrians, clothing manufacturers commonly produce bright clothing to make the wearer more conspicuous. Manufacturers also regularly secure retroreflective articles to the outer surface of the clothing to improve wearer conspicuity. Retroreflective articles are passive devices that return incident light back toward the light source. The articles highlight a person""s presence to motorists at nighttime by reflecting light from the motor vehicle""s headlamps back to the motor vehicle driver. The bright image displayed by the retroreflective article ultimately gives motorists more time to react.
Sometimes the retroreflective articles are colored for aesthetic reasons or to provide enhanced contrast for better daytime visibility. Frequently, fluorescent colors are used in conjunction with retroreflective sheeting to make the sheeting more conspicuous under daytime viewing conditions (see, for example, U.S. patent application Ser. No. 08/587,339 pending or corresponding International Publication WO 95/31739 and U.S. Pat. Nos. 3,830,682, 5,387,458, and 5,695,853).
Because retroreflective articles are regularly used on clothing, they must be able to withstand laundering conditionsxe2x80x94otherwise, the articles cannot continue to serve their safety function after repeated washings. Investigators at the 3M Company who design retroreflective articles for use on clothing are aware of this problem, and they have developed launderably-durable retroreflective articles so that persons who wear retroreflective clothing remain conspicuously visible after their clothing has been laundered many times. U.S. Pat. Nos. 5,200,262, 5,283,101, 5,474,827, 5,645,938, 5,738,746, and 5,812,317 disclose examples of launderably durable retroreflective articles developed at 3M. These products typically comprise optical elements that are partially embedded in a specially formulated binder layer.
Investigators also recognize that the need to develop launderably durable retroreflective articles is particularly pronounced for clothing that regularly is worn in harsh environments. Examples of such clothing include firemen""s jackets and construction workers"" safety vests (see, for example, U.S. Pat. No. 4,533,592 to Bingham). These garments tend to get very dirty, very often, and therefore they are frequently cleaned under industrial laundering conditions. Industrial laundering conditions involve wash temperatures as high as 40 to 90xc2x0 C. (105 to 190xc2x0 F.) and pH values of 10 to 13. Some of the launderably durable retroreflective articles disclosed in the 3M patents mentioned above are capable of withstanding the more stringent industrial wash conditions.
In some retroreflective articles, a colored appearance has been achieved by placing a colored polymeric layer on top of the optical elements. Retroreflective articles that contain optical elements partially embedded in a polymeric top layer (also referred to as a cover film) are commonly referred to as xe2x80x9cenclosed lensxe2x80x9d retroreflective articles. In addition to providing color, the polymeric top film allows the article to be easily wiped clean, and the articles generally exhibit good retroreflectivity when wet. Examples of patents that disclose colored top films include U.S. Pat. Nos. 5,069,964 and 5,378,520. In these retroreflective articles, a dye or pigment is added to the top film. Commercially available products that have a colored top film include 3M Scotchlite(trademark) 7960 and 7987 brand products.
An alternative to enclosed lens retroreflective articles are xe2x80x9cexposed lensxe2x80x9d retroreflective articles, which have the optical elements exposed to the ambient environmentxe2x80x94that is, the optical elements are not covered by a polymeric top film. These articles generally include an exposed layer of transparent microspheres, a polymeric binder layer, and a reflective layer. The transparent microspheres are partially embedded in the binder layer and are partially exposed to the atmosphere, and the reflective layer is generally disposed between the microspheres and the binder layer.
Another kind of retroreflective article is an xe2x80x9cencapsulated lensxe2x80x9d retroreflective article. These articles are similar to enclosed lens articles in that they employ a top film over the layer of microspheres. Encapsulated lens retroreflective articles, however, differ from enclosed lens articles by having the top film encapsulate a pocket of air above the layer of microspheres. U.S. Pat. No. 4,025,159 to McGrath, U.S. Pat. No. 4,896,943 to Tolliver et al., U.S. Pat. No. 4,897,136 to Bailey et al., and U.S. Pat. No. 5,069,964 to Tolliver et al. disclose examples of encapsulated lens type products. In one variation of an encapsulated lens retroreflective sheeting (disclosed by Tung et al. in U.S. Pat. No. 4,678,695), transparent microspheres are partially embedded in a binder layer, and a clear or colored top film is disposed over the microspheres. The binder layer may impregnated with a white pigment, or, alternatively, with a colored pigment to make a sheeting that displays a corresponding daytime color and exhibits nighttime reflection.
These three systems, exposed lens, enclosed lens, and encapsulated lens sheetings, have various advantages and disadvantages relative to one another, and coloring techniques applicable to one system are not necessarily applicable to the other. Exposed lens articles tend to be more flexible and simpler in construction but cannot be colored simply by including a dye in a top film because the articles have no top film. Enclosed lens and encapsulated lens articles, while being somewhat easier to color, generally suffer from the drawback of not being very useful at high temperatures because the polymeric top film can melt. Enclosed lens and encapsulated lens articles, therefore, do not rate as high as exposed lens articles when considering candidate for the use on firefighters"" jackets.
A variety of methods, however, have been employed to impart color to exposed lens retroreflective articles. In U.S. Pat. No. 3,700,305, for example, Bingham discloses an exposed lens retroreflective article that has alternating layers of different refractive index dielectric materials coated on glass microspheres. A colored layer, such as a fluorescent layer, is applied behind the dielectric reflector. Because the dielectric reflector is essentially transparent under daytime viewing conditions, the fluorescent layer imparts a daytime fluorescent color to the article. Under nighttime or retroreflective viewing conditions, however, the article is basically incapable of displaying the color of the underlying colored layer because incident light never strikes that layer: it is first reflected by the dielectric reflector back towards the light source. The patent is silent regarding durability under home wash or industrial laundering conditions.
Other methods of coloring an exposed lens retroreflective article are discussed briefly in U.S. Pat. Nos. 3,758,192, 4,102,562, and 5,200,262. In U.S. Pat. No. 3,758,192, Bingham discloses an exposed lens retroreflective article that has transparent microspheres partially embedded in a binder layer that contains flakes of nacreous (pearlescent) pigment and other various pigments or dyes. While this product can display a colored retroreflective image, there is nothing in the patent which shows that the product would be industrial wash durable. In U.S. Pat. No. 4,102,562 to Harper et al., an exposed lens retroreflective article is disclosed that can display a colored imagewise pattern. The article has transparent microspheres coated with a transparent dielectric mirror prepared as described in U.S. Pat. No. 3,700,305 to Bingham. An ink layer that contains a pigment and a melamine is applied behind the reflective layer (see Example 2). Harper et al. state that the melamine reacts with the epoxide moiety of the adhesion promoting silane (see Example 2). Because the ink layer is disposed behind the reflective layer, the article, while being able to display the colored image under daytime viewing conditions, is not capable of displaying a colored retroreflective image. The patent also does not show that the retroreflective articles would be durable under industrial wash conditions. Wu-Shyong Li, in U.S. Pat. No. 5,200,262, partially embeds transparent microspheres in a binder layer that may be colored by a pigment or dye, preferably a black dye such as a chromium-azo dye. Li suggests the use of a metal layer or dielectric material as a reflector. The reflector is located on the embedded portion of the transparent microspheres. When a metal reflector is used, the color of the underlying binder layer is not noticeable under daytime or nighttime viewing conditions. And when a dielectric reflector is used, the color of the underlying binder layer is not noticeable under nighttime (i.e., retroreflective) viewing conditions. Li""s product is, however, designed to withstand industrial wash conditions.
Ulf Olsen, in U.S. Pat. Nos. 5,344,705, 5,503,906, and 5,620,613, discloses exposed lens retroreflective articles that have a color layer printed on the embedded portion of a layer of transparent microspheres. The color layer typically contains a transparent pigment or dye that is substantially uniformly dispersed in a transparent resin. The color layer is disposed between the microspheres and a reflective layer, which reflective layer comprises reflective flakes in a transparent resin. Olsen also discloses that the color layer and the reflective layer may be replaced by a colored reflective layer comprising both colorant and reflective flakes in a transparent resin. While this product can display a colored image under retroreflective conditions, it does not indicate that good wash durability would be achieved under industrial conditions.
In U.S. Pat. Nos. 5,510,178, 5,612,119, 5,679,198, and 5,785,790, Ulf Olsen describes an exposed lens retroreflective product that has an imagewise colored coating disposed behind a transparent dielectric mirror that is coated on the backside of microspheres partially embedded in a binder layer. The colored image in this product is, however, not noticeable under retroreflective conditions; it can only be seen under daytime lighting conditions.
The present invention provides a new, exposed lens retroreflective article that can exhibit color under retroreflective conditions and that can demonstrate extraordinary durability under industrial wash conditions. In brief summary, the inventive exposed lens retroreflective article comprises: a layer of optical elements, a colored layer, a binder layer, and a reflective layer. The optical elements are partially embedded in the binder layer, and the colored layer and the reflective layer are disposed behind the layer of optical elements such that incident light first passes through the colored layer before striking the reflective layer. The reflective layer is located functionally behind the optical elements to make it capable of returning incident light back into the optical elements. The colored layer is colored by a dye that is covalently bonded to a polymer. Unlike conventional color layers, which contain pigments or dyes that are physically suspended within a polymer matrix, the dye in the colored layer of the present invention is connected to the polymer molecule by a covalent bond.
In another aspect, the present invention provides a new transfer for supplying a retroreflective article to a garment assembler. In a further aspect, the invention provides an article of clothing that has the inventive retroreflective article disposed on its outer surface.
The colored, exposed lens, retroreflective articles of the invention differ from known exposed lens articles by having the dye covalently bonded to the polymer in the colored layer and by placing this colored layer between the optical elements and the reflective layer. The inventive retroreflective articles can demonstrate improved durability in that they maintain retroreflectivity and their original color even after multiple episodes of industrial laundering. The color durability of these articles, as compared to articles employing conventional dyes or pigments, is believed to result from the covalent bond(s) that connect the dye to the polymer. These relatively high strength bonds can make the dyes resistant to dissociation from the polymer and consequent extraction from the retroreflective article. The improved laundering durability makes the inventive retroreflective articles particularly suitable for use on safety garments such as utility, construction, and sanitation workers"" garments.
The placement of the colored layer between the optical elements and the binder layer enables a colored image to be seen under both daytime and retroreflective conditions. Light striking the front surface of the retroreflective article passes through the colored layer before and after it is reflected by the reflective layer. This enables a viewer of the retroreflected light to see the color of the colored layer. The color is also noticeable under daytime viewing conditions because the colored layer can be seen beneath the layer of transparent optical elements.
In reference to the invention, the following terms have the meanings set forth below:
A xe2x80x9cbinder layerxe2x80x9d is a polymeric layer that provides assistance in structurally supporting a layer of partially embedded optical elements.
A xe2x80x9ccolored layerxe2x80x9d is a layer that is not colorless or clear.
xe2x80x9cCovalent bondsxe2x80x9d are those bonds in which valence electrons are shared, examples include carbon-carbon, carbon-nitrogen, and carbon-oxygen bonds.
A xe2x80x9cchromophorexe2x80x9d means any chemical group, such as the azo group, that gives color to a compound.
A xe2x80x9cdyexe2x80x9d is an organic or organometallic molecule or moiety that contains a chromophore that absorbs light of a particular wavelength(s) to impart color to the colored layer. In the inventive retroreflective article, the dye shares covalent bond(s) with a polymer.
The language xe2x80x9cfunctionally behindxe2x80x9d means that the reflective layer is positioned relative to the layer of optical elements such that the reflective layer is capable of reflecting incident light back into the optical elements.
xe2x80x9cExposed lens retroreflective articlesxe2x80x9d are retroreflective articles that have optical elements partially embedded in the retroreflective article and partially exposed to the atmosphere.
xe2x80x9cOptical elementsxe2x80x9d are light transmissive elements capable of affecting the direction of light that enters the elements so that the light ultimately can be returned toward the light source.
xe2x80x9cPolymerxe2x80x9d means a molecule that is made up of at least five repeating units that are regularly or irregularly arranged.
xe2x80x9cPolymericxe2x80x9d means containing a polymer.
xe2x80x9cRetroreflectivexe2x80x9d means having the characteristic that obliquely incident incoming light is reflected in a direction antiparallel (180 degrees) to the incident direction, or nearly so, such that an observer at or near the light source can detect the reflected light.
A xe2x80x9creflective layerxe2x80x9d is a layer that is capable of reflecting incident light so that it can reenter the optical elements.